SECONDARY STORAGE DEVICES

SECONDARY STORAGE DEVICES are used for the long term storage of data. Data is commonly stored using magnetic or optical material. Magnetic materials may have their polarity easily changed with the application of an outside magnetic field. Optical materials may have thier physical structure and optical propertices change by the application of light and/or a magnetic field. Magnetic media are the most common form of storage today. Optical technology is becoming more efficient and readily accessible and may replace magnetic storage in smaller computers. A read/write head is used in both types to either read data from or write data to a storage medium.

Common magnetic storage devices are magnetic tape drives, disk packs, hard disk drives, and floppy disks.
Magnetic tapes store data sequentially. Tapes must be searched from beginning to end to find the desired data. Disks however store and retrieve data randomly as the read/write head moves from the edge to the hub of a disk and the disk rotates.

Secondary storage media is useless until it is FORMATTED. When a magnetic disk is formatted, four regions are created on the disk. A BOOT AREA is created so that the disk has enough programs on it to commmunicate with the operating system. The FAT, FILE ALLOCATION TABLE is used so to keep data like the name, location, and properties of all the files on the disk. A ROOT DIRECTORY is created as the highest directory in the file structure of the disk. And a DATA AREA is created to contain all the data the user adds to the disk.
PARTITIONING is a process like formatting in which the data areas are designated for specific purposes and or uses. This
is usually done to hard disk drives before the INSTALLation of software.

Optical disk media are normally formatted to have one continuous spiral track from the hub to the edge of the disk.

READ WRITE HEADS are used to store and retrieve data from tapes or disks. Magnetic read write heads change the polarity of the sectors of a disk. Optical read write heads may change the shape and/or the charge of the media. In larger systems, the read write heads are arranged between the disks or platters. The disks are staked atop each other.

The demand for larger capacity secondary storage never ceases. Magnetic storage devices for pcs have grown from 8" 5 MB and 5 1/4" 1.2 MB disks to 3 1/2" 1.44 MB, 2.88 MB, 100 MB and 200 MB disks. Similarly optical devices are storing more in less space.
The physical limitations on capacity are challenges which will continually be overcome as new materials and manufacturing methods develop.
Optical disks are used when a lot of data needs to be stored in a small portable space. Many different types of devices from cell phones/fax/pagers to specialty tools and calculators are designed to accept either dense packages of magnetic memory or small CD-ROMs or CD-Rs to enhance the capability of these devices.

The internet is also being used as a secondary storage device for many businesses. They keep their records on a remote site via the internet. This method saves the data even if there is a local fire or other disaster which ruins the local hardware or software.